A lubricant is a substance, usually organic, introduced to reduce friction between surfaces in mutual contact, which ultimately reduces the heat generated when the surfaces move. It may also have the function of transmitting forces, transporting foreign particles, or heating or cooling the surfaces. The property of reducing friction is known as lubricity.

In addition to industrial applications, lubricants are used for many other purposes. Other uses include cooking, bio-medical applications on humans, ultrasound examination, medical examinations, and the use of personal lubricant for sexual purposes.

Lubicants have been in some use for thousands of years. Calcium soaps have been identified on the axles of chariots dated to 1400 BC. Building stones were slid on oil-impregrated lumber in the time of the pyramids. In the Roman era, lubricants were based on olive oil and rapeseed oil, and well as animal fats. The growth of lubrication accelerated in the Industrial Revolution with the accompanying use of metal-based machinery.

Relying initially on natural oils, needs for such machinery shifted toward petroleum-based materials early in the 1900s. A breakthrough came with the development of vacuum distillation of petroleum, as described by the Vacuum Oil Company. This technology allowed the purification of very nonvolatile substances, which are common in many lubricants.

Non-liquid lubricants include grease, powders,PTFE tape used in plumbing, air cushion and others. Dry lubricants such as graphite, molybdenum disulphide and tungsten disulphide also offer lubrication at temperatures (up to 350 °C) higher than liquid and oil-based lubricants are able to operate.

A large number of additives are used to impart performance characteristics to the lubricants. Typical lubicants contain one or more. Automotive lubricants contain as many as ten additives, comprising 20% of the lube.